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An alternative Senator Loudspeaker System . . . . . . for the budget conscious Did you fantasise about the Senator loudspeakers described in our September 2015 issue? They are certainly impressive, both in appearance and performance. But there is no denying that they are beyond the budget of many readers. Now there is money to be saved, by employing a lower cost woofer and tweeter from Altronics. And you can also save money if you decide to build your own cabinet. W e know that many readers were impressed with the Senators but were dismayed at the cost. The high performance Celestions drivers are quite expensive and then you have the cost of the Bunnings Kaboodle cabinet. The Kaboodle cabinets certainly have an impressive appearance and professional finish but they bring the all-up cost to around $1700 for a pair. The performance from the package 36  Silicon Chip easily matches that of far more expensive big name loudspeakers with similar characteristics but with prices ranging up to as much as $25,000! So prompted by appeals from readers, we decided to assess what could be achieved with lower cost, locally available loudspeakers. It did not take long before a woofer By Allan Linton-Smith in the Altronics range looked like a reasonable prospect. Sure, it does not have the extreme efficiency and high power handling of the specified 10-inch woofer from Celestion but not everyone wants or needs a loudspeaker capable of a maximum sound pressure level (SPL) of 118dB at one metre – this is extremely loud! The Altronics woofer in question is their C 3026 which is quoted as having a frequency response from 28Hz to siliconchip.com.au On the left is the budget version of the Senator with the Altronics 10-inch woofer and 1-inch dome tweeter. They perform well but our preference is for the combination on the right with the Celestion horn tweeter teamed with the Altronics woofer. These cabinets are based on the original Bunnings “Kaboodle” kitchen system – as you can see, these have a highly reflective gloss finish. You can save quite a bit of money by cutting your own panels from MDF and applying your own finish, as detailed in this article. siliconchip.com.au May 2016  37 +30 Altronics Senator Speaker Frequency Response 20/01/2016 08:42 +25 +20 +15 Relative Amplitude (dBr) +10 Altronics Tweeter & Woofer Celestion Tweeter/Altronics Woofer +5 HF Boost +0 Celestion Tweeter & Woofer -5 No HF Boost -10 -15 -20 -25 -30 -35 -40 10 20 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz) 50 Altronics Senator Speaker Distortion 20/01/2016 08:41 20 Altronics Tweeter & Woofer 10 Celestion Tweeter/Altronics Woofer Total Harmonic Distortion (%) 5 2 1 0.5 0.2 Celestion Tweeter & Woofer 0.1 0.05 0.02 0.01 20 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz) Altronics Senator Speaker Impedance 20/01/2016 08:37 60 50 Celestion Tweeter/Altronics Woofer Impedance (Ohms) 40 Celestion Tweeter & Woofer 30 Dotted line indicates effect of treble boost network 20 10 Altronics Tweeter & Woofer 0 10 20 50 100 200 500 Frequency (Hz) 38  Silicon Chip 1k 2k 5k 10k 20k Fig.1 shows the frequency response of the two speaker combinations. The blue curve is the response using the Altronics C 3026 woofer combined with the Celestion CDX11730 compression tweeter, mated with the Celestion T1534 horn. The green curve shows the performance with the Altronics 1-inch dome tweeter which gives a rising response to around 11kHz. Fig.2 shows the harmonic distortion of the two driver combinations, together with the distortion curve for the original Senator featured in the September 2015 issue (pink trace). The red curve is the combination of the Altronics woofer and Celestion tweeter and it is really quite comparable, especially when the lower cost is considered. Fig.3 shows the impedance curves of both versions of the budget Senator speakers together with the impedance curve of the original Senator design. None of these will cause any problems for typical hifi amplifiers. 4kHz (with no dB limits), a maximum power handling of 120 watts and an efficiency of 93dB/1W <at> 1m. So its power handling is about 4dB down on the Celestion woofer and its efficiency is 3dB less. That still means that the substitute woofer is capable of very high sound levels in the average lounge room. And the cost for the Altronics woofer? Just $79, including GST. Now you can still team the Altronics woofer with the Celestion horn tweeter or you can save more money by substituting the Altronics C 3004 1-inch dome tweeter. This has the same efficiency as the suggested Altronics woofer and a rated frequency response from 2kHz to 20kHz (again, with no dB limits). It is much cheaper than the Celestion horn tweeter at $49.50 including GST. Our preference is for the combination of the Celestion horn tweeter and the Altronics woofer and that is backed up by the measured performance, however the choice is up to you. Performance Fig.1 shows the frequency response of the two speaker combinations. As you can see, we achieved a very respectable frequency response using the Altronics C 3026 woofer combined with the Celestion CDX1-1730 compression tweeter, mated with the Celestion T1534 horn. There are dips around the 500Hz & 1kHz regions but these are simply not noticeable for most types of music. The Celestion tweeter is silky smooth and is really unbeatable on violin strings and cymbals. The response curve shows the effect of the HF boost facility and this worth doing (if your ears are good enough to perceive the difference!). We also tested the Altronics woofer combined with the Altronics C 3004 tweeter and as can seen, the tweeter is somewhat on the bright side. Treble boost is certainly not required. Hence our overall preference is for the Celestion horn tweeter. As already noted, the efficiency of the budget line-up is only a tad less, -3dB, compared to the original Senator but we confirmed it as 93dB/1W <at> 1m – and that is still very high compared to the majority of high fidelity loudspeakers which are often rated at as little as only 86dB/1W <at> 1m. That 7dB difference means that siliconchip.com.au SIDE A SIDE A FRONT A 730 x 417mm 730 x 417mm 730 x 300mm SIDE B SIDE B FRONT B 730 x 417mm 730 x 417mm 730 x 300mm NOTE: Tweeter cutout dimensions are to suit CELESTION horn; for Altronics tweeter cut 73mm diam hole. REAR A TOP A 730 x 300mm 417 x 336mm REAR B 730 x 300mm TOP B BASE A BASE B 300 x 381mm 300 x 381mm 417 x 336mm MATERIAL: 2400 x 1200 x 18mm MDF etc. Fig.4: the build-it-yourself version of the Budget Senator can (just!) be cut from a standard sheet of 18mm MDF, with the exception of the reflector board. Fig.5: this “exploded” view shows how the panels (which must be very accurately cut) fit together. Not shown here is the 280 x 414mm internal reflector board, which can be virtually any stiff board such as 10mm MDF or even plywood. It is fitted to the rear baffle before the top is glued and screwed on. our budget Senator will potentially be louder with a 50 watt per channel amplifier than a 200W/channel amplifier feeding a typical hifi loudspeaker system. And remember that many smaller hifi loudspeakers probably couldn’t handle anywhere near 200 watts anyway! The harmonic distortion of our pre- ferred budget Senator loudspeaker system (Altronics woofer + Celestion tweeter) is also very respectable. Fig.2 shows three distortion curves. The pink trace is the distortion curve for the original Senator featured in the September 2015 issue. The red curve shows the combination of the Altronics woofer and Celestion tweeter and it is really quite comparable, SILICON CHIP ONLINESHOP especially when the lower cost is considered. The orange curve shows the combination of Altronics woofer and tweeter and again, you can see why we prefer the Celestion tweeter. Finally, Fig.3 shows the impedance curves of both versions of budget Senator together with the impedance curve of the original Senator design and none . . . it’s the shop that never closes! 24 hours a day, 7 days a week . . . it’s the shop that has all recent S ILICON C HIP PCBs – in stock . . . it’s the shop that has those hard-to-get bits for S ILICON C HIP projects . . . it’s the shop that has all titles in the S ILICON C HIP library available! . . . it’s the shop where you can place an order for a subscription (printed or on-line) from anywhere in the world! . . . it’s the shop where you can pay online, by email, by mail or by phone Browse online now at www.siliconchip.com.au/shop siliconchip.com.au May 2016  39 320 of these will cause any problems for 30 typical hifi amplifiers. Cabinet construction Whichever speaker combination you choose, the biggest saving to be made is by building the cabinets from scratch instead of basing them on the Bunnings Kaboodles. If you take the Kaboodle approach, the overall cost will be about $600 for a pair of cabinets, depending on the chosen finish. For many constructors, the Kaboodle approach will be the easiest and one which assures a very good presentation. Your spouse will love it. However, if you can make your cabinet, there is quite a lot of money to be saved. The cabinets can be made of plywood, MDF (medium density fibreboard) or veneered chipboard, with a minimum thickness of 18mm. A single sheet of 2400 x 1200 x 18mm MDF (also known as craftwood) shouldn’t cost you much more than $30-$35 – plus any cutting costs, of course. The biggest hurdle for most people in this process is getting the timber panels precisely cut. One solution is to go to your local Bunnings Warehouse. They can supply 18mm MDF and a 2400 x 1200mm sheet will suffice for two cabinets – see TWEETER TWEETER JAYCAR HANDLE POCKET 120 100 140 280 720 730 REFLECTOR 280 x 415mm WOOFER WOOFER TERMINAL PLATE CROSSOVER PCB 233 DIAM PORT (88mm ID) 90 150 150 SIDE VIEW ALL DIMENSIONS IN mm 330 PORT 90 DIAM C L 100 FRONT VIEW Fig.6: these diagrams are for the D-I-Y version made from MDF or similar and cut to size. The reflector panel needs to be fixed in place (again, with glue and screws) before the top is screwed/glued on. The reflector panel, which is not as wide as the box (ie, there are air gaps between the reflector and the box sides), also makes an ideal place to mount the crossover (which we will look at in detail next month). Wiring goes from the terminal to the crossover PCB thence to the tweeter and woofer. Senator Budget Speaker Specifications Power Handling: up to 60W RMS (AES standard, continuous pink noise) Sensitivity: 93dB / 1 watt <at> 1m Frequency Response: ±6dB 45Hz-20kHz Distortion: THD+N ~1% at 1kHz; <2% 250Hz-20kHz; <0.5% 1.2kHz-18kHz <10% 35Hz-20kHz Impedance: more than 6from 10Hz-20kHz Woofer: Altronics C 3026 10” Tweeter: Celestion CDX1-1730 compression driver, mated with a Celestion T1534 horn Crossover: 2-way first order (6dB/octave slope) 40  Silicon Chip siliconchip.com.au note below. Better still, most Bunnings Warehouse stores can offer a cutting service (for a fee) so you can get all the panels cut precisely. Fig.4 shows our suggested cutting arrangement for a 2400 x 1200 x 18mm panel. By the way, do not be tempted to use thinner MDF, plywood or even timber. We are suggesting 18mm as the minimum thickness, to avoid the need for panel bracing to stop resonances. If you want a really rigid cabinet, go for 25mm thick MDF. It will be heavier but the resulting cabinet should be completely non-resonant. One downside: using 25mm MDF will almost certainly mean that you won’t get all the panels from a single 2400 x 1200 sheet, so apart from the higher cost of 25mm MDF, you’ll need more of it! The dimensions of the cut panels need to be changed to suit 25mm. If you do not have a Bunnings Warehouse in your region, we suggest that you get a local kitchen cabinet maker to cut the panels. They have the ability to cut panels with great precision and they can also supply the required MDF, 18mm or 25mm thick. They can also cut the required holes in the front and rear panels and they may even be able to assemble the cabinets for you but make sure you find out the cost before telling them to proceed. Once you have the panels cut, the traditional approach is to glue and screw them together with the aid of timber cleats which help with panel Just to show the results which can be achieved, this photo shows a pair of bookshelf speakers also made from MDF and finished with coats of gloss paint. If you take care and prepare the surfaces properly, you can achieve a very satisfactory result with this approach. We warn you about using a paintbrush, though: you cannot get the brush strokes out! Use a roller – or even better, a spray gun. (See SILICON CHIP, November 2006). siliconchip.com.au Fig.7: a rendition of a completed enclosure using the lower-cost method of construction, where all 18mm panels are cut from a sheet of 2400 x 1200mm MDF. If you decide to use 25mm-thick panels instead (which will undoubtedly give a better result) you won’t get all panels from a single sheet. The reflector board is never seen so it can be cut from just about anything you can lay your hands on between about 10 and 18mm thick. alignment. But we have devised an assembly procedure which dispenses with cleats. The tools required are a few quick release clamps sufficiently large to span the width of the cabinet, an electric drill and tube of PVA glue. In fact, if you have a willing assistant, you may be able to dispense with clamps as well. The exploded cabinet diagram of Fig.5 shows how it all goes together. In essence, you start with the base panel (measuring 284 x 381mm) and proceed to wrap the front baffle, sides and back panel around. So place the base panel on plastic. Then drill and countersink holes for 32mm chipboard screws in each of the four panels, as shown in Fig.5 Then run a bead of PVA glue along the mating surface of all four panels. If you have an assistant, he or she can hold each panel vertical and butted up to the base panel while you drive home the screws. (The screws are merely to hold the panels together while the glue sets). If you don’t have an assistant, then you will need to use clamps and in May 2016  41 Building the boxes using the Kaboodle approach . . . For a much more detailed procedure, refer to the original Kaboodle-based Senator Speakers article in the September 2015 issue  Note: reflector panel is not shown. that case, we would suggest glueing all the panels together in one fell swoop. It is easier to do, provided you have sufficient clamps to do the job. The alternative, gluing panels together in sequence, means that you have to be absolutely sure that each panel is exactly at right angles to its neighbour and that the edges are correctly aligned; otherwise the panels will not fit. Also make sure that you position the baffle and rear panels correctly, otherwise one or both will end up being upside-down. The final step is to glue and screw the top panel in place but before you do that, the 280 x 415mm reflector panel must be fitted as shown in Fig.5. You can do this with a combination of chipboard screws and PVA glue as shown in cabinet side elevations diagram – see Fig.6. Before fitting the reflector panel, it’s a good idea to mount the completed crossover board on it and attach the wires, including those which run to the rear panel terminals. Or, at the very least, mark and drill the crossover board mounting holes. Once you have all panels glued and 42  Silicon Chip After assembling the carcase, the front panel goes on, with holes cut out to exactly match those on the inner panel... poke the speaker wires through the appropriate holes, ready for the drivers to be mounted when the boxes are complete. screwed together, wipe off any excess PVA glue while it is still wet. Once dry, it is virtually impossible to remove and you will have to sand any excess flat – which spoils the very smooth finish of the panels. Leave the cabinet(s) to dry overnight. Making them look good OK, while your bare MDF cabinets may be strong, rigid and non-resonant, they will not be objects of beauty. You need to finish them off. How you do that is up to you but we can describe one method we used to finish similar MDF cabinets in the November 2006 issue. On that occasion, we used a router bit to machine a 5mm radius on all the corners of the cabinet. This removes the very sharp edges on the panels and the end result looks much better. Having done that, there are a number of options for finishing your cabinets and this must be done before the drivers and terminals are installed. The approach we used was to paint the cabinets using a high gloss, oil-based enamel.  Next, the two side panels are glued into place. Make sure you wipe up any excess sealant before it cures. By the way, it’s better to leave the protective plastic on the panels until the boxes are finished. We started by using an all-purpose acrylic primer, after having thoroughly sanded off all the rough edges. We also used an acrylic filler to fill the inevitable fine gaps in the joins between the panels and also fill in the countersunk screw holes. Don’t make the same mistake we made when painting the panels. Do not use a brush – you will never get rid of the brush marks. Instead, use a roller intended for applying gloss paint – we learnt by doing! (This assumes you don’t have a spray gun, which will give by far the best finish if you know what you’re doing!). After thoroughly sanding it all back, we then used a 50mm foam roller to apply the finish coat. This gives much better results and while you won’t get the glass-smooth finish that is attainable with a spray gun, it is much quicker and easier. The slightly dimpled finish from the foam roller is also better at hiding any surface blemishes. Kaboodle cabinets For many readers, making and finishing their own cabinets will simply siliconchip.com.au 433mm   The top panel as supplied is too long, so it needs to be (very carefully!) cut to size (433mm deep) and smoothed off. When this is done, the top panel can be glued into position, chamfered edges up. It sits flush with the front surface but indented slightly (about 8mm) on each side. be too hard and not worth the trouble. They will want to take the Kaboodle approach and for those readers we will repeat the main assembly steps, as shown in the illustrations above. For readers who want more details, you will need to refer to the article in Budget the September 2015 issue. First step in the Kaboodle process is to assemble the carcase of the 450mm wide cabinet, shown above. This shows the finished carcase which is open on one side, apart from the addition of a 417 x 135 x 15mm MDF brace. We then cut the holes in what will be the front panel for the tweeter, woofer and bass reflex port. We also cut the holes in what will be the rear panel for the terminal plate and the hand-hold (very handy for lifting the rather heavy finished enclosure). Senator Speaker Parts List Timber requirements Cut-your-own-panel version: 1 2400 x 1200mm sheet 18mm MDF OR (for 25mm MDF) as above plus 1 1200 x 1200mm sheet 1 reflector panel 280 x 415mm x ~10-18mm MDF, ply, etc Paint etc for desired finish Kaboodle version: Kaboodle 450mm wall cabinet (Bunnings Part No W-51623) (16mm HMR panels) 2 end panels (Bunnings: Seduction Red part no D65744)* 1 door (Bunnings Seduction Red part no D65699)* 1 shelf (becomes angled reflector panel) 415 x 280mm 1 side support (113 x 417mm, 16mm MDF or DAR timber) * Other colours will have different part numbers # Available from Electric Factory (www.elfa.com.au) siliconchip.com.au Here’s what your finished Senator speaker boxes should look like, immediately before mounting the drivers in the holes. The back and underneath are not covered by Kaboodle dress panels; they’re the only ones that aren’t. Other components required 2 10” woofers (Altronics C 3026) 2 compression drivers (Celestion CDX1-1730#) or tweeters (Altronics C 3004) 2 horns (Celestion T1534# – not required with Altronics tweeters) 2 150mm offcuts of 90mm PVC stormwater pipe 2 terminal plates (Jaycar PT3012) 2 handle pockets (Jaycar HS8012) 8 legs to suit (Bunnings 100mm chrome “Leggz”, pack of 4) 4 rolls acrylic fibre (wadding) 700 x 1000mm (Jaycar AX3694) 2 crossover PCB assemblies (see next month) 1 cartridge of neutral-cure silicone sealant/caulking compound ~4m heavy-duty figure-8 polarised speaker wire ~50 40-50mm 10G woodscrews (countersunk head) 16 10g 40mm stainless woodscrews Miscellaneous screws to suit terminal plates, crossover PCBs and hand-holds May 2016  43 The Speaker Drivers We Used . . . Apart from the saving in building the speaker boxes from MDF, one of the major cost-saving changes in this version of the Senator speakers is the use of a significantly cheaper woofer – in this case, the Redback (Altronics) C 3026. While not quite as good a performer as the original Celestion woofer (and it must be said, a much lower power handling capability), listening tests at the same relative power levels convinced us that the average person would be hard-pressed to tell the difference between the two woofers. While there is also a significantly lower-cost tweeter and As you proceed, there are a few important points to keep in mind: Leave the protective plastic coating on the Kaboodle gloss dress panels until the enclosures are complete and all the hardware (speakers, crossover PCB etc) are installed. That will minimise scratches and damage from any “oopses”. Be especially careful not to drop screwdrivers or other tools onto the dress panels. All joins must include a bead of silicone sealant to ensure they are airtight. We used bathroom caulking compound which has very good adhesive properties. It is good because it allows you move panels slightly to get the position just right but once it has set, it is extremely strong. After all, a similar method is used to assemble aquarium tanks. Too much sealant is better than not enough – but be careful to clean up any excess as you go. The longer you leave it, the harder it will be remove. Openings for the woofers and tweeters need to be cut in the “door” panels. You will need to cut holes in the cabinet carcase for the loudspeakers etc and you will also need to cut corresponding holes in the front panel for the loudspeakers and the bass reflex port. 44  Silicon Chip horn also available in the Redback range, we still prefer the silky-smooth Celestion CDX1-1730 compression tweeter and T1534 horn combination used in the original Senators. Therefore, we have based this design on the Redback woofer and the Celestion tweeter/horn. Most people will not require the very high powerhandling capability of the original design – the Budget Senator fed by a typical hifi amplifier is more than enough! These holes are best cut with a jigsaw from the “back” side for best results (so that the gloss exterior finish is not likely to be scratched). The same comment applies when you need to cut a side panel slightly shorter to act as the top of the cabinet. You will need some 15mm MDF or particle board cut to the dimensions given in the relevant diagram parts list to make up the side support panel. The four adjustable feet supplied with the Kaboodle kit should be left in their packing until the enclosure is finished and the hardware mounted. The Kaboodle shelf should not be discarded as it is used to make the angled reflector panel inside the enclosure. The driver units are mounted using stainless steel screws 10G x 1825mm, countersunk head. They are the last items to be fitted. Next month We’ll conclude the assembly of the Budget Senator speakers with details of the crossover, as well as tying up some loose ends (such as wiring, fitting feet, etc). SC The rear panel of the Kaboodle version showing the input terminal (bottom) and the pocket handle (top). MDF version has these components in the same relative positions. siliconchip.com.au